Many gases have their characteristic infrared absorption wavelengths in the infrared spectrum region. One known apparatus for measuring a particular gas utilizing this characteristic is a non-dispersive infrared (NDIR) gas measuring apparatus. Such a gas measuring apparatus is composed mainly of an infrared light source, a gas cell, a band-pass optical filter, and an infrared sensor.
An infrared sensor described in Patent Document 1 (Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2000-503122) includes a detector that includes a narrow band-pass optical filter that transmits infrared light having an absorption wavelength of a target gas, and two detectors that include band-pass optical filters that transmit two reference wavelengths different from the absorption wavelength of the target gas. The concentration of a sample gas can be measured by processing the output signals of these three detectors.
Patent Document 2 (Japanese Unexamined Patent Application Publication No. 2013-113692) and Patent Document 3 (Japanese Unexamined Patent Application Publication No. 2012-220419) disclose a thermal infrared sensor for use in NDIR gas measuring apparatuses. A thermal infrared sensor disclosed in Patent Document 2 is a pyroelectric infrared sensor composed of a pyroelectric material layer formed of an aluminum nitride piezoelectric material and a pair of electrodes disposed on each side of the pyroelectric material layer. Patent Document 3 discloses that a pyroelectric infrared sensor contains a ceramic material, such as PbTiO3, Pb(Zr,Ti)O3 (PZT), or Pb(Zr,Ti)O3—Pb(Mn,Nb)O3 (PZT-PMN), a single crystal material, such as LiTaO3 or LiNbO3, or a polymeric material, such as PVF2, as a material of a pyroelectric material layer.
Patent Document 1: Japanese Unexamined Patent Application Publication (Translation of PCT Application) No. 2000-503122
Patent Document 2: Japanese Unexamined Patent Application Publication No. 2013-113692
Patent Document 3: Japanese Unexamined Patent Application Publication No. 2012-220419